CVE-2025-6386: Lollms Timing Attack Auth Bypass Flaw

CVE-2025-6386 Overview

CVE-2025-6386 is a timing attack vulnerability in the parisneo/lollms repository. The flaw resides in the authenticate_user function inside lollms_authentication.py. The function uses Python's default string equality operator to compare passwords, which exits at the first character mismatch. Attackers can measure response time differences to enumerate valid usernames and recover passwords character by character. The issue is fixed in version 20.1. This vulnerability is classified under [CWE-203] Observable Discrepancy.

Critical Impact

Remote attackers can enumerate valid usernames and incrementally recover passwords by analyzing authentication response timing, leading to full account compromise without prior credentials.

Affected Products

• parisneo/lollms repository versions prior to 20.1
• lollms_authentication.py authentication module
• LoLLMs (Lord of Large Language Models) Web UI deployments using built-in authentication

Discovery Timeline

• 2025-07-07 - CVE-2025-6386 published to NVD
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-6386

Vulnerability Analysis

The vulnerability exists in the authenticate_user function of lollms_authentication.py. The function compares submitted passwords against stored values using Python's standard == operator. This operator performs a sequential, character-by-character comparison and short-circuits when it encounters the first non-matching character. The execution time therefore correlates with the number of leading characters that match the expected value.

An attacker on the network can submit authentication attempts and measure the time the server takes to respond. Requests with passwords sharing more initial characters with the real value take measurably longer to fail. By iterating across the character space at each position, an attacker reconstructs the password incrementally. The same technique applies to username enumeration when the authentication path returns early for unknown accounts.

The vulnerability requires no authentication, no user interaction, and is exploitable remotely over the network. It only impacts confidentiality, but credential disclosure typically enables follow-on attacks against the application.

Root Cause

The root cause is the use of a non-constant-time string comparison for security-sensitive secrets. Python's == operator is optimized for performance, not constant-time evaluation. Authentication code must use comparison primitives such as hmac.compare_digest, which run in time dependent on the input length rather than content. The parisneo/lollms maintainers addressed this in commit f78437f7b5aa39a78c6201912faf4e0645a38c48.

Attack Vector

Attackers send a high volume of authentication requests to the lollms endpoint while measuring server response time. Statistical analysis of latency distributions reveals which candidate characters produce slower failures, indicating partial matches. The attacker advances one character at a time until the full password is recovered. Network jitter is mitigated by repeated sampling and percentile analysis. See the Huntr Bounty Report and GitHub Commit Details for technical details.

Detection Methods for CVE-2025-6386

Indicators of Compromise

• High volume of failed authentication attempts from a single source against /lollms authentication endpoints over short intervals.
• Sequential authentication requests with passwords that vary by a single trailing character.
• Unusual request patterns showing systematic enumeration of username space prior to password attempts.
• Sustained low-rate authentication probing designed to evade rate limits while collecting timing samples.

Detection Strategies

• Instrument the authentication endpoint to log per-request latency and flag clients whose request distribution suggests timing measurement.
• Alert on authentication request rates exceeding human-plausible thresholds from any single client IP or session.
• Correlate failed login bursts with subsequent successful logins from the same source as an indicator of recovered credentials.

Monitoring Recommendations

• Forward lollms web server access and authentication logs to a centralized logging or SIEM platform for retention and analysis.
• Track response time variance on authentication endpoints and baseline normal latency to detect anomalous probing.
• Monitor for password spray and credential stuffing signatures originating against the LoLLMs deployment.

How to Mitigate CVE-2025-6386

Immediate Actions Required

• Upgrade parisneo/lollms to version 20.1 or later, which replaces the vulnerable comparison logic.
• Force a password reset for all existing accounts to invalidate any credentials that may have been recovered.
• Restrict network exposure of the LoLLMs interface to trusted networks or place it behind an authenticating reverse proxy.

Patch Information

The fix is included in parisneo/lollms version 20.1. The remediating change is documented in commit f78437f7b5aa39a78c6201912faf4e0645a38c48. Review the GitHub Commit Details to verify the constant-time comparison logic before redeploying.

Workarounds

• Enforce strict rate limiting and account lockout on the authentication endpoint to reduce the feasibility of timing measurement.
• Place the LoLLMs service behind a VPN or zero-trust network access gateway to remove unauthenticated network reachability.
• Add randomized response delays in front of the authentication endpoint as a temporary measure until the upgrade is applied.

# Upgrade lollms to the patched release
pip install --upgrade lollms==20.1

# Verify installed version
python -c "import lollms; print(lollms.__version__)"